The introduction of portable computing devices such as laptop computers and the development of sophisticated presentation software for use on computers has resulted in a need for similarly compact and portable projection devices for use in what is commonly known as an electronic presentation. One early and still common manner of projecting an electronic presentation has been the use of a liquid crystal display (LCD) panel, such as illustrated in U.S. Pat. No. 4,719,547, on a conventional overhead projector (OHP). These panels are electronically addressable, i.e., the appearance of the final image is controlled by electronic signals sent to the panel. The electronic signals may come from a computer, or may be standard video (NTSC) signals, or from other suitable devices.
The use of such a LCD panel is illustrated in U.S. Pat. Nos. 5,231,434 and 4,846,694. The LCD panel and the overhead projector are independent devices used together for the duration of the presentation only. The LCD panel is placed on the overhead projector stage, and light passing from the stage through the LCD panel is projected onto a viewing surface by the overhead projector.
As the convenience of electronically generated and stored presentations has become appreciated, a new class of presentation devices has appeared, often referred to as "integrated projectors." An integrated projector unit is capable of taking input from a computer or other signal source and projecting an image onto a screen. Modern integrated projectors are capable of projecting useful images even in high ambient light conditions. Such units have developed a patent literature of their own, a few examples of which are outlined below.
U.S. Pat. No. 4,943,154 shows a projector that has three "light valves" (a particular form of an addressable liquid crystal display), and a complicated optical path intended to allow the output of a white-light source to be split into red, green and blue components, imaged with the three light valves (one for each color) and then recombined for projection through a single lens. Such optical systems are complicated to manufacture, assemble and maintain, occupy a considerable amount of space, weigh a substantial amount, and have potential efficiency problems. Other examples of this type of device are illustrated in U.S. Pat. Nos. 5,374,968 and 4,018,509.
An alternative method of projecting an image is to have a single LCD panel, optical path, and lens, and interpose in succession red, green and blue filters. As each filter moves into the optical path, the appropriate color image is formed on the LCD. Such units have been limited by the ability of the LCD to rapidly respond to changing input signals. They also need a well engineered filter wheel and associated hardware. For these reasons this method has found little use.
It is also possible to use what is known as a three-color LCD. This panel has an array of micro-filters (red, green and blue) printed onto the face of the display, and these filters are addressed appropriately by the liquid crystal array mounted to register with them. This type of LCD, while slightly more complicated to manufacture, has the advantage of needing only a single optical system. In addition, the filters and control elements can never lose alignment, and the weight of the LCD need be little more than the weight of a single color unit, thus economizing on weight and space. Additional weight savings are also achieved in the elimination of prisms, filters, mirrors, etc., and their mounts.
U.S. Pat. No. 5,321,450 describes a projector exemplifying these principles. By the use of mirrors and an angled LCD, a low profile is achieved. A lens having its optical axis vertically disposed is used for projection, and a final mirror (that can be folded down) redirects the light along a horizontal path. This mirror is the only component that is moved for storage, and the space savings is minor. Another such device is illustrated in U.S. Pat. No. 4,971,436 which shows a light source, a transmission LCD panel and a projection lens. Also illustrated in this patent are folded optics which are desirable to reduce the total volume or footprint of the unit.
There are limitations to further size reduction in these devices. As requirements for high brightness projectors evolve, more powerful light sources must be incorporated. When powerful sources are to be incorporated into small-sized devices, problems arise over the removal of waste heat (generated by most light sources, and particularly by Tungsten filament, quartzhalogen and arc sources). Thus, efficient heat removal systems must be designed. Also, there is a very substantial danger that the heat generated by the light source will cause a degradation of the performance of sensitive electronic components needed for the operation of these devices. U.S. Pat. No. 5,313,234 addresses this problem by having designed "hot" and "cold" compartments. The lamp source and cooling means are contained in the "hot" compartment, while the LCD panel and the projection lens are contained in the "cold" compartment.
Related and co-pending applications U.S. Ser. No. 08/673,292, U.S. Ser. No. 08/623,729 and U.S. Ser. No. 08/787,075, owned by the assignee of the present application, disclose further ways to reduce the size of such projectors. U.S. Ser. No. 08/673,292 discloses an efficient lamp cooling means that permits the placement of LCD panels in close proximity to powerful light sources. U.S. Ser. No. 08/623,729 and U.S. Ser. No. 08/787,075 disclose means for rotating the LCD between a storage position and an operative position, thereby reducing the storage volume of the projector. It is possible, by these means, to produce conveniently sized projectors which are easily portable and still capable of excellent optical performance.
However, as the size of integrated projectors decreases, new problems arise. In particular, the close proximity of sensitive electronic components and powerful light sources provides the opportunity for undesired electromagnetic and thermal interactions to occur between the components. These interactions are capable of degrading the performance of the projector system to such an extent that it is unacceptable for high quality presentations.
It would therefore be desirable and advantageous to devise a compact and portable integrated projector which took advantage of unused space within the projector, which minimized electromagnetic and thermal interference between components, and which allows for quick and easy deployment for use.